1. Technical Field
The invention relates generally to an improved vehicle suspension system. More particularly, the invention relates to air spring suspension systems with parallelogram components for land vehicles. Specifically, the invention relates to a parallelogram style suspension system with an independent, full parallelogram suspension at each wheel.
2. Background Information
Suspensions are available in the prior art which utilize air springs to provide a comfortable ride, even for large over-the-road trucks and other heavy vehicles. The air springs are typically used in industrial vehicle single axle units tandem or multi-axle arrangements of two or more axles which are either driven or non-driven.
One drawback of air spring suspensions is that an air spring is essentially an air inflated bag and requires auxiliary stabilization. An air suspended axle must have separate independent mechanical location and attitude controls and stabilized components or it will not function. Absent stabilization, the air spring will extend to its maximum length or width in the direction of least resistance. Also, uneven transverse load distribution on a vehicle supported on unstable air springs will cause vehicle lean and tip-over.
A significant number of air spring suspensions have been developed which to a greater or lesser extent, control axle location and attitude. A number of suspensions that have been developed are roll rigid, while others are roll flexible, each generally being designed for a specific application. The most common roll rigid configuration is the trailing beam type suspension, most of which use the axle as a torsion rod to provide roll rigidity.
Another type of suspension which has been developed is the parallelogram suspension which is not inherently roll rigid, and does not inherently provide lateral stiffness. Again, ancillary devices such as an anti-roll bar, track bars, or guide mechanisms have been utilized to stabilize typical parallelogram designs. As such, parallelogram type suspensions, even with the ancillary devices attached, were often only suitable for low center of gravity loads, or on specialized vehicles stabilized by other vehicle suspension mechanisms.
Trailing arm suspensions are brake reactive. That is, when the vehicle brakes are applied, the suspension will tend to compress thereby reducing the suspensions effectiveness. Similarly, when the brakes are applied as the vehicle moves in reverse, the suspension will tend to raise up, and pivot about the single trailing arm pivot, again reducing the suspensions effectiveness. Further, most trailing arm suspensions suffer from dock walk such that they move toward or away from the loading dock as the suspension moves up or down with the brakes locked. This movement is caused from air draining off the air springs, or as a result of loads added to or removed from the vehicle, or the temperature changes that occur as the trailer remains parked by the dock. Dock walk occurs, primarily because of rotation of the beam, axle and tire assembly when the brakes are locked. As the suspension travels vertically with the brakes locked it rotates the tires causing the tires to move the vehicle horizontally. If the trailer is positioned adjacent a dock, it causes the trailer to move toward or away from the dock as a result of the movement or rotation about the single pivot point.
Similarly, trailing arm suspensions do not utilize the air springs full capacity as the air spring plates are not parallel in extreme operating positions, again as a result of the trailing arm pivoting about a single pivot point.
Parallelogram suspensions were developed to solve a number of the problems associated with trailing arm type suspensions. However, parallelogram suspensions create problems not present in trailing arm type suspensions. Specifically, parallelogram suspensions are not inherently roll rigid or provide lateral stiffness. Parallelogram suspensions have been found to be a significant advancement over the prior art as they provide a relatively stable, safe, and comfortable ride for all types of loads. Some of these parallelogram suspensions are included in U.S. Pat. Nos. 4,114,923, 4,132,432 and 4,309,045.
Advantages of the parallelogram type air spring suspensions include that the air suspended axle in a parallelogram suspension moves a very short linear distance between the loaded and unloaded positions and has no rotational component to the motion. This reduces the problem of dock walk inherent in trailing arm type suspensions.
Further, the parallelogram stabilized suspension permits the air spring's full-load capacity to be utilized. The top and bottom air spring plates remain substantially parallel throughout the full range of air spring travel whether the vehicle is fully loaded or unloaded. Specifically, when the air spring is mounted on the parallel moving link of the parallelogram it allows the utilization of the air springs full travel and full load capacity. In comparison, in the typical trailing arm design where the air spring travels in an arc and “fans” open stretching the rearmost fibers of the spring while not utilizing even the full travel of the forward part of the air spring.
Parallelogram type suspensions are also typically not brake reactive. That is, they do not dive or raise when brake torque is applied to the suspension system.
The parallelogram suspension inherently provides the above advantages, and also locates the axle relative to the longitudinal axis of the vehicle by controlling the forward and rearward motion of the axle relative to the frame. Moreover, a parallelogram suspension also controls the path which the air spring follows as it operates to take up irregularities in the road surface.
Therefore, a need exists for an air spring suspension which incorporates the benefits of a parallelogram suspension, an independent wheel suspension, and an air ride suspension.